Changing the color group of an Svg emits repaintNeeded which will then
cause it to schedule a pixmap update anyway. Includes a unittest.
REVIEW: 127313
source should always return the same value as it was assigned.
Also removed duplicated code (empty sourceString is now handled
as if the source couldn't be converted to any type).
REVIEW: 127282
Add some tests for IconItem.
Also found one issue in animation when quickly changing source, first frame
will be rendered with wrong icon.
REVIEW: 127103
